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Hindawi Publishing CorporationJournal of Skin CancerVolume 2012, Article ID 147863, 9 pagesdoi:10.1155/2012/147863

Research Article

Topical Curcumin-Based Cream Is Equivalent to DietaryCurcumin in a Skin Cancer Model

Kunal Sonavane,1 Jeffrey Phillips,1 Oleksandr Ekshyyan,1, 2 Tara Moore-Medlin,1, 2

Jennifer Roberts Gill,3 Xiaohua Rong,1, 2 Raghunatha Reddy Lakshmaiah,1 Fleurette Abreo,4

Douglas Boudreaux,5 John L. Clifford,3 and Cherie-Ann O. Nathan1, 2, 6

1 Department of Otolaryngology-Head and Neck Surgery, Louisiana State University Health Sciences Center, Shreveport,LA 71130-3932, USA

2 Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, LA 71130-3932, USA3 Department of Biochemistry, Louisiana State University Health Sciences Center, Shreveport, LA 71130-3932, USA4 Department of Pathology, Louisiana State University Health Sciences Center, Shreveport, LA 71130-3932, USA5 Boudreaux’s Compounding Pharmacy, Shreveport, LA 71130-3932, USA6 Department of Surgery, Overton Brooks VA Medical Center, Shreveport, LA 71130-3932, USA

Correspondence should be addressed to Cherie-Ann O. Nathan, [email protected]

Received 7 September 2012; Accepted 20 November 2012

Academic Editor: Ajit K. Verma

Copyright © 2012 Kunal Sonavane et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Skin squamous cell carcinoma (SCC), the most common cancer in the USA, is a growing problem with the use of tanning boothscausing sun-damaged skin. Antiproliferative effects of curcumin were demonstrated in an aggressive skin cancer cell line SRB12-p9(P < 0.05 compared to control). Topical formulation was as effective as oral curcumin at suppressing tumor growth in a mouseskin cancer model. Curcumin at 15 mg administered by oral, topical, or combined formulation significantly reduced tumor growthcompared to control (P = 0.004). Inhibition of pAKT, pS6, p-4EBP1, pSTAT3, and pERK1/2 was noted in SRB12-p9 cells post-curcumin treatment compared to control (P < 0.05). Inhibition of pSTAT3 and pERK1/2 was also noted in curcumin-treatedgroups in vivo. IHC analysis revealed human tumor specimens that expressed significantly more activated pERK (P = 0.006)and pS6 (P < 0.0001) than normal skin samples. This is the first study to compare topical curcumin to oral curcumin. Our datasupports the use of curcumin as a chemopreventive for skin SCC where condemned skin is a significant problem. Preventionstrategies offer the best hope of future health care costs in a disease that is increasing in incidence due to increased sun exposure.

1. Introduction

The American Cancer Society estimates that 1–1.3 millioncases of nonmelanoma skin cancer (NMSC) will be detectedannually. Cutaneous SCC accounts for nearly 20% of allskin cancers, and excluding melanoma, 75% of all deathsattributed to skin cancers [1]. Unlike the more prevalentbasal cell carcinoma (BCC), SCC is an aggressive tumorthat metastasizes with a frequency as high as 12.5% [2].Prevalence is common in fair complexion Caucasians withlower reported rates in individuals with darker complexionsincluding Asians and Africans. Cutaneous SCC of the faceoften metastasizes to parotid lymph nodes, which can be

detrimental to the facial nerve during treatment and nodesin the neck, as the head and neck are rich in lymphaticnetworks. Treatment for NMSC may include cryotherapy,electrosurgery, topical 5-fluorouracil, photodynamic ther-apy, imiquimod, and radiation therapy; however, surgicalintervention is the primary treatment modality. Whentreated early, the five-year cure rate is greater than 90%[3]. NMSC recurrence varies from 8–16%, second lesionrecurrence rates are as high as 75% within the first twoyears and 95% within five years [3]. This suggests a windowof opportunity for chemopreventive agents to delay orprevent a recurrence or metastatic spread. Lymph nodemetastasis in NMSC varies from 0.1 to 28%, with a resulting

2 Journal of Skin Cancer

mortality from 50–75% [4]. Overall five-year survival ratesfor regional lymph node metastasis are 25–35% [3, 5–7] andless than 20% at ten years [1]. Early cancer detection offersthe best window of opportunity for treatment. Early stageskin cancer has a high cure rate, whereas advanced stagecutaneous SCC often develops resistance to chemotherapy.Therefore, research has focused on developing these novelchemopreventive agents to delay or prevent cutaneous SCCformation.

Curcumin, an extract from the Indian spice turmeric, hasbeen investigated in a variety of human cancers includingpancreatic, prostate, breast, and head and neck cancer.The first published report demonstrating the topical useof curcumin in cancer reported a sustainable reduction inlesion size and pain [8]. Curcumin has antioxidant, anti-inflammatory, antiangiogenic and anticarcinogenic activity,although its clinical use is limited by low bioavailability [9].

More recently, several studies have examined curcumin’seffect in inhibiting skin carcinogenesis. Additionally, numer-ous reports have identified signaling pathways related toepidermal growth factor receptor (EGFR) that are essentialto formation and progression of cutaneous malignancy. TheMTOR and MEK/ERK signaling cascades are two of themost well-studied pathways [10]. In a prior study by ourgroup [11] we subcutaneously injected immunodeficientmice with SRB12-p9 skin SCC and demonstrated thatcurcumin administered by oral gavage significantly inhibitedtumor growth and downregulated pS6, a well-establisheddownstream biomarker of the MTOR and MEK/ERK path-ways. Curcumin’s anti-carcinogenic effects have been linkedto inhibition of the MEK/ERK signaling pathway in breastcarcinogenesis, and researchers continue to explore thesepotential biomarkers in other cancers [12]. However, ERKsactivity in cutaneous malignancy is not well defined inthe literature. Hence, we wanted to determine if topicalcurcumin was as efficacious as oral curcumin in a SCCskin xenograft model and elucidate the pathways down-regulated by curcumin as potential biomarkers for futurechemopreventive studies with our topical curcumin cream.In addition, we wanted to observe the potentially additiveeffects of topical application and oral dosing. We also wishedto explore whether the MEK/ERK pathway is overexpressedin human cutaneous SCC and BCC in the hope of identifyinga novel intracellular target at which curcumin may act toinhibit tumorigenesis. We hypothesized that pERK and itsdownstream target pS6 would be overexpressed in cutaneousskin cancers given its role in promoting cellular proliferationin aggressive malignancy. Identifying intermediate endpointsis necessary to assess intervention results for primary cancerprevention and address problems with feasibility posed bylarge patient numbers, length of study, and cost when canceroccurrence or recurrence is an endpoint [13].

2. Materials and Methods

2.1. Curcumin. Curcumin C3 Complex (>98% pure) wasobtained from Sabinsa Corp. In vivo studies were conductedwith curcumin (15 mg) suspended in vehicle (100 μL corn

oil) for oral gavage feeding or suspended in a vanishingcream paste (15 mg/100 μL cream) for topical administrationprovided by our study compounding pharmacist (DB).

2.2. Cell Lines and Xenografts. The human skin SCC cellline SRB12-p9 was derived by single-cell cloning fromaggressive skin SCC SRB12 cells (a gift from Dr. ReubenLotan, Department of Thoracic Head and Neck MedicalOncology, University of Texas M.D. Anderson Cancer Centerin 2003) and was cultured as described [14]. This cell line waschosen due to its sensitivity to curcumin as evidenced in cellculture studies. DNA was isolated from the cell lines using acommercially available DNA purification kit (Qiagen). DNAsample was sent to Genetica (Cincinnati, OH, USA), and thecell line was validated by DNA profiling.

2.3. Cell Proliferation. 2,000 SRB12-p9 cells per well wereseeded in triplicate onto 96 well plates in complete mediaat 37◦C with 5% CO2. After adherence, cells were treatedwith curcumin (0–40 μM) for 0–72 hours. Cell viability wasmeasured using MTS (Promega).

2.4. Subcutaneous HNSCC Xenograft Model. Studies wereconducted in accordance with the Declaration of Helsinki(1964) and in compliance with Louisiana State UniversityHealth Sciences Center Institutional Animal Care and UseCommittee guidelines. Animals housed in a barrier facilitywere maintained on a normal diet ad lib. Forty 6–8-week-old Severe Combined Immunodeficiency (SCID) micewere shaved and pretreated with either 0 mg (corn oil),15 mg curcumin by oral gavage, 15 mg curcumin topicalpaste, or combined 15 mg oral gavage and 15 mg curcumintopical paste once daily for 3 days prior to squamous cellcarcinoma xenograft injection (n = 10 per group). Micewere then injected subcutaneously with 1 × 106 SRB12-p9cells suspended in sterile PBS (Day 0). All mice continueddaily treatment with either 0 mg or 15 mg curcumin bygavage, topical, or both, and tumors were measured dailywith digital calipers. Xenograft tumors did not form inone animal per group and were excluded (n = 9 pergroup). Tumor volume (mm3) was calculated using thefollowing formula: (0.52 × length2 × width). Body weightwas measured daily, and mice were monitored for adverseeffects from the experiment. Daily oral gavage and tumorvolume measurement continued through day 29, at whichtime tumors were harvested after the mice were anesthetizedwith isoflurane and sacrificed. Ex vivo tumor volume wascalculated using the following formula: (4/3π0.5 × length ×0.5 × width × 0.5 × height). The study pathologist (FA)measured maximum skin thickness, including the stratumcorneum but not the granular layer.

2.5. ELISA. Pooled serum from mice (n = 3/group) wasanalyzed by enzyme-linked immunosorbent assay (ELISA,BD Bioscience) according to the manufacturer’s instructions,to assess expression of human and murine IL6. Sampleswere analyzed in duplicate for IL-6 expression with aspectrophotometric plate reader.

Journal of Skin Cancer 3

2.6. Immunohistochemical Analysis of Molecular Markers inSkin Squamous Cell Carcinoma. Tumors harvested on day 29were embedded in paraffin, sectioned, and H&E stained forconfirmation of squamous cell carcinoma presence by ourstudy pathologist (FA). Tumors (n = 3 per group) were thenstained with phospho-ERK (cell signaling, Thr202/Tyr204;1 : 600) and phospho-STAT3 (cell signaling, Tyr705; 1 : 200)as previously described [15, 16]. Subcellular localizationwas determined by immunofluorescence. Paraffin sectionsof tumors with overlying mouse skin were probed withpERK1/2 and pSTAT3 antibodies (Cell Signaling) followedby an Alexa-546-labeled secondary antibody.

Human actinic keratosis, skin SCC, and BCC paraffin-embedded blocks were sectioned and stained with phospho-p44/42 MAPK (ERK 1/2) rabbit monoclonal antibody(Thr202/Tyr204, 1 : 600) and phospho-S6 ribosomal proteinrabbit monoclonal antibody (Ser235/236, 1 : 100) as previ-ously described [17–19] and read by our study pathologist(FA). Specimens were scored based on the intensity ofantibody nuclear and cytoplasmic staining in each slide, withabsence of staining scored as a [0], weak or focal stainingscored as a [+], and strong staining with a [++].

2.7. Western Blot Analysis. Soluble proteins extracted fromSRB12-p9 cell lysates treated with 0 μM or 20 μM curcuminfor 24 hours or xenograft tumors were analyzed by westernblot as previously described [19]. Proteins were detectedusing enhanced chemiluminescence (Amersham PharmaciaBiotech, Piscataway, NJ, USA) and analyzed with Image-Quant TL7.0 (GE Healthcare) software (n = 6/group).The following antibodies from cell signaling were used:AKT (1 : 200), phospho-AKT (Ser473; 1 : 100), S6 ribosomalprotein (1 : 500), phospho-S6 ribosomal protein (Ser235/236;1 : 500), STAT3 (1 : 200), phospho-STAT3 (Tyr705; 1 : 200),4EBP1 (1 : 200), phospho-4EBP1 (Ser65; 1 : 200), ERK1/2(1 : 200), phospho-ERK1/2 (Thr202/Tyr204; 1 : 200), and actin(1 : 3500).

2.8. Patient Tissue Samples and Controls. All BCC and SCCtissue samples were obtained from patients recently diag-nosed with nonmelanoma skin cancer of the face orneck, after obtaining approval by the institutional reviewboard and obtaining informed consent from all subjects.Patients were treated primarily with surgical resection atLouisiana State University Health Shreveport and the Over-ton Brooks Veterans Administration Hospital from 2009to 2011. Formalin-fixed, paraffin-embedded tissue blockswere obtained from 27 BCC tissue samples, 4 ActinicKeratosis (AK) tissue samples, and 17 SCC tissue samples(from 16 SCC patients). Normal human skin samples weresurgically obtained from uninvolved adjacent skin in patientsundergoing resection for skin cancer. Total of 25 normal(noncancer) skin samples were analyzed in the study. Several5 μm slides were cut from each tissue block, and oneslide was stained with hematoxylin and eosin (H&E) andreviewed by a pathologist to confirm pathologic findingsand assess surgical margins. All other slides were used forimmunohistochemical staining.

2.9. Statistics Applied for the Analysis. Proliferating cell per-centages were compared using one-way analysis of variance(ANOVA). One-way ANOVA was also used to determinesignificant differences in skin thickness and the differencesbetween individual treatment groups. A Tukey’s multiplecomparison as a post hoc test was performed to eval-uate differences between treatment groups. Tukey’s post-hoc testing, Chi-square test for independence, or Fisher’sexact probability test was used to determine the abilityof pERK and pS6 expression to correlate with cutaneousSCC, differentiate tumor types from normal skin and BCC,and determine if there was a significant difference betweenpERK and pS6 staining and the different types of histologiccutaneous lesions. Paired t-test was used to determinesignificant difference in biomarker expression by westernblot analysis.

3. Results

3.1. Growth Inhibitory Effects of Curcumin In Vitro and InVivo. To determine whether a skin SCC cell line is sensitiveto curcumin, a cell proliferation assay was performed onSRB12-p9 SCC cell line. Curcumin’s growth inhibitoryeffects in the aggressive skin cancer cell line (SRB12-p9)were noted as early as day 2 at 20 μM (P < 0.05)curcumin compared to control. Curcumin treatment at doses20 μM and 40 μM was significantly effective in inhibiting theproliferation of SRB12-p9 cells compared to control on days2 and 3 (P < 0.05; Figure 1(a)).

Curcumin appears to inhibit growth compared to controlin SRB12-p9 xenograft tumors after tumor cells had achance to engraft (Figure 1(b)). There was a significant effectfor curcumin treatment (F(3, 96) = 11.58, P < 0.001)in suppressing growth of the SRB12-p9 xenograft tumors.Tukey’s post hoc comparisons of the four groups indicatetumor volume from the gavage group (M = 44.55, 95%CI [35.77, 53.77]) and the combined group (M = 88.81 CI[71.73, 105.89]) was significantly smaller than the controlgroup tumor volume (M = 191.35, 95% CI [127.12,255.59]), P < 0.001. The topical group (M = 130.66, 95% CI[95.29, 166.04]) tumor volume was also statistically smallerthan the control group tumor volume (P = 0.02). There wasno difference between the gavage group tumor volume andthe topical group tumor volume (P = 0.19).

Because invasive tumors could give inaccurate measure-ments and overlying skin could influence in vivo tumor mea-surements, we also measured tumors ex vivo and measuredskin thickness (Figure 1(c)). There was a significant effectof curcumin on ex vivo tumor volume (F(3, 32) = 5.49,P = 0.004). Tukey’s post hoc comparisons of the four groupsindicate that the tumor volumes from the gavage group (M =72.06, 95% CI [37.78, 106.35]), topical group (M = 195.82,95% CI [71.59, 320.05]), and combined group (M = 152.32,95% CI [101.048, 203.60]) were significantly smaller than thecontrol (M = 416.77, 95% CI [161.48, 672.06]), P < 0.001,P = 0.006 and 0.02, respectively. There was a significanteffect for curcumin treatment on tumor mass (F(3, 32) =5.79, P = 0.003), where the gavage group (M = 0.043, 95%


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Figure 1: Curcumin inhibits skin SCC cell growth in vitro and in vivo. (a) Cell proliferation of the aggressive skin cancer cell line SRB12-p9after treatment with 0–40 μM curcumin. ∗P < 0.05 versus control group; ∗∗P < 0.01 versus control group; ∗∗∗P < 0.001 versus controlgroup. (b) Mice were pretreated with the indicated dose of curcumin for 3 days prior to injection with 1 × 106 SRB12-p9 tumor cells in thedorsal region (day 0) and continued receiving daily curcumin treatment (9 mice per group, mean tumor volume± SD). Tukey’s post hoc test:∗P < 0.05 versus control group; ∗∗∗P < 0.001 versus control group. (c) Representative images of xenograft tumors at harvest and ex vivofrom the indicated treatment groups.

CI [0.02, 0.07]), topical group (M = 0.112, 95% CI [0.041,0.184]), and combined treatment group tumors (M = 0.076,95% CI [M = 0.050, 0.101]) were significantly smallerthan that of the control group (M = 0.244, 95% CI [0.09,0.39]) tumors, P < 0.001, P = 0.02, and 0.003, respectively.There was no difference in skin thickness in mice treatedwith curcumin by gavage, topical, and combined groupscompared to the control group (P = 0.73).

3.2. Curcumin’s Effects on Signaling Pathways. We next eval-uated curcumin’s effects on signaling pathways in the aggres-sive skin cancer cell line (SRB12-p9) in vitro. Using a concen-tration that significantly inhibited cell growth (20 μM), therewas significant inhibition of pAKT, pS6, p-4EBP1, pSTAT3,and pERK1/2 (Figure 2). As can be seen in Figure 2 therewas about twofold inhibition in the phosphorylation of theaforementioned markers in SRB12-p9 cells after curcumintreatment.

We next evaluated curcumin’s effects on signaling path-ways in xenograft tumors using western blot analysis

(Figure 3). Among the tested biomarkers an inhibition ofpERK1/2 was noted in the curcumin-treated groups, whereasinhibition of pSTAT3 was only noted in the combinedcurcumin group (Figure 3(a)).

As western blot analysis involves homogenization oftotal tumor tissue, such as stroma and infiltrating hostinflammatory cells, we also evaluated curcumin’s effectson signaling pathways by immunohistochemistry, whichcan distinguish nonviable and nontumor components, suchas stroma, that are not included in the scoring of thebiomarker analyzed. IHC results revealed strong positivepERK staining throughout tumors in the control groupand weaker, focal staining in the curcumin-treated tumors(Figure 3(b)). Immunofluorescence confirmed curcumin’seffects on pERK and a shift in the subcellular localization ofthe activated state of STAT3 in the topical group compared tothe control group (Figure 3(c)). Curcumin is known for itsanti-inflammatory effects. Therefore, we evaluated its effectson the inflammatory marker IL6 in all curcumin treatmentgroups using pooled serum samples. The levels of soluble


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Figure 2: Curcumin’s effects on AKT/MTOR and ERK pathways in vitro. (a) Western blot of SRB12-p9 tumor cells treated with (+) orwithout (−) 20 μM curcumin for 24 hours and probed with the indicated antibody. Representative Western blots for two analyzed setsare shown. (b) Band densities of indicated biomarkers (n = 6) were quantified using ImageQuant software and normalized to actin proteinlevel. Data presented as Mean± SE. ∗ Indicates P < 0.05 versus vehicle-treated control. A significant inhibition of expression of the followingbiomarkers was observed: pAKT (P = 0.0368); pS6 (P = 0.0182); p4EBP1 (P = 0.0098); pSTAT3 (P < 0.0001); pERK1/2 (P = 0.0313). a.u.:arbitrary units.

IL6 were the lowest in the topical curcumin group, whilecurcumin did not affect IL6 levels in the gavage or combinedgroups (Figure 3(d)).

3.3. Patient Characteristics. Patient demographics and clini-cal characteristics are summarized in Table 1. Tissue samplesfrom 46 male patients and 4 female patients were analyzed.Age ranged from 39 to 93 with a mean age of 66 ± 14years. There was no difference in age between the groups byANOVA (F = 1.272, P = 0.29). The large majority of patientswere white, except for one African American patient withalbinism. Nonmelanoma skin cancers analyzed were excisedfrom the external nasal skin (14), cheeks (14), ears (9), scalpand forehead (13), neck, chin, and lip (6). No skin site wasoverrepresented in analysis.

3.4. IHC Analysis of Patient Tissues. The presence and inten-sity of pERK and pS6 staining in all SCC, BCC, and normaltissue samples were compared (Table 2). All SCC specimens(n = 17, 100%) stained positive for phosphorylated ERK,while only 10 of 27 (37%) BCC samples stained positive.Although all the normal skin samples stained weakly positive

(grade 1+) for activated pERK in the stroma, palisadingcells, and epithelium (n = 24, 100%), significantly moreSCC specimens showed strong staining with pERK (grade2+) than normal skin (P = 0.0028, Table 2 and Figure 4).However, the majority of BCC specimens (17/27, 63%)showed no pERK staining (P < 0.0001 compared to normalskin).

Most specimens containing SCC (n = 13, 81%) andBCC (n = 16; 64%) showed strong staining (grade 2+) foractivated pS6, while all the analyzed normal skin specimens(n = 8; 100%) demonstrated negative pS6 staining. Tumorspecimens expressed significantly more activated pS6 thannormal skin samples (1+ score and above; P < 0.0001;Figure 4). Skin cancer type significantly predicted intensityof pERK staining, as SCC tumors stained more intensely forpERK than the background stroma in normal skin and BCCtumor cells (P < 0.0001; Figure 4). When pERK expressionwas analyzed and compared to other demographic factors,the variance in pERK expression scores correlated signifi-cantly with tumor type, R2 = 0.25, P = 0.0007. Patientage (P = 0.85) and gender (P = 0.35) did not explain thevariance in pERK staining.


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Figure 3: Curcumin’s effects on the ERK pathway in vivo. (a) Western blot of pooled xenograft tumors (n = 6/group) of the indicatedantibody. (b) The presence and intensity of pERK staining (brown) in the control group compared to the presence and intensity of pERKstaining in the curcumin-treated xenograft tumors. (c) Representative IHC staining of SRB-12 p9 WT cell tumor xenografts. Paraffin sectionsof tumors were probed with STAT3 phospho-Tyr705 (pSTAT3, top row) or ERK1/2 phospho-Thr202/Tyr204 (pERK, bottom row), followedby an Alexa546-labeled secondary antibody (400x). (d) IL-6 ELISA of pooled mouse serum (n = 3/group) in duplicate.

4. Discussion

Identifying consistent intracellular biomarkers at which apotential chemopreventive may act is essential prior toinitiating clinical trials. As curcumin acts on many differentbiomolecular targets in a variety of different cell types it isimportant to determine if curcumin directly affects eithera few major downstream biomarkers or a multiplicity ofdownstream targets which may serve to explain curcumin’svarying effects in different cell types. Aberrant signalingthrough the epidermal growth factor receptor (EGFR) playsa major role in cutaneous skin cancer progression. EGFRinhibitors have been used for SCC therapy to downregulateaberrant EGFR signaling with little change in overall survival[20], possibly due to compensating mutations downstreamof EGFR. One of these signaling pathways is PI3 K/AKT

that plays a role in skin carcinogenesis and in chemotherapyresistance [21].

Activated Ras/Raf signaling has also been implicated in asmall percentage of SCC [22] and can lead to activation of theMAPK pathway. Ras/Raf gain-of-function can occur throughactivation of ERK1 and ERK2, which are constitutively activein 70% of malignant melanoma due to RAS or BRAFactivating mutations [2]. Activated ERK1/2 is rarely seen innormal skin specimens but is shown in all cases of SCC witha positive association with the degree of malignancy andproliferative activity of SCC [23]. In this study, Zhang et al.looked at 10 well-differentiated and 10 poorly differentiatedskin SCC cases. Another study looked at activated ERK in 101human head and neck squamous carcinoma specimens [24].Therefore, inhibiting ERK may be a promising approachin targeted cutaneous skin SCC therapy. Having previously


Table 1: Clinical and demographic patient characteristics.

Total Normal∗ AK SCC BCC P value

Gender∗∗

Male 46 21 4 14 250.77∗∗∗

Female 4 4 0 2 2

Race

White 49 24 4 15 270.57∗∗∗

African American 1 1 0 1 0

Age

70 19 5 2 6 11

Skin site

Nose 14 6 2 2 8

0.71∗∗∗Cheeks 14 7 0 8 6

Ear 9 5 1 1 5

Scalp and forehead 13 5 1 5 5

Other 7 4 0 2 3∗

Normal skin samples were surgically obtained from uninvolved adjacent skin in patients undergoing resection for skin cancer.∗∗Some patients had more than one type of cancer and are counted in both groups.∗∗∗No significant difference in number of males and females, race, age, or skin site distribution per group by Fisher’s exact test.

Table 2: Summary of pERK and pS6 IHC staining in normal (noncancer), AK, BCC, and SCC skin samples.

[0] [1+] [2+] P value∗ Total

pERK staining

Normal Skin 0 24 0 24

AK 0 4 0 1.0000 4

BCC 17 5 5


pERK1/2

pS6

Normal AK BCC SCC

Figure 4: IHC analysis of pS6 and pERK expression in patients with negative (blue) staining and strong positive (brown) staining of tumorcells with pERK and pS6. Normal patient skin samples with minimal background staining and normal appearing cells. Representativeactinic keratosis (AK) patient samples showing weak, cytoplasmic staining. Representative BCC patient samples with negative (blue) stainingand few scattered positive (brown) staining of tumor cells. Representative SCC patient samples with strong positive (brown) nuclear andcytoplasmic staining with pERK and pS6. Note that the stroma stains positive (brown) in BCC, whereas the tumor stains negative (blue).

compared to control. IL6 plays a central role in regulating theinflammatory response [25]. Because IL-6 may contributeto angiogenesis and metastasis [26], inhibition of IL-6 withtopical curcumin suggests a mechanism of chemoprevention.Although curcumin has previously been shown to inhibitIL-6 in HNSCC cell lines [27], this is the first skin cancermodel investigating curcumin’s inhibition of systemic IL-6. The present study demonstrates that topical curcuminreduces skin SCC tumor growth, and this effect might beexplained, by the inhibition of IL-6.

In this study we demonstrated significant inhibition ofseveral biomarkers of the AKT/mTOR pathway as well asSTAT3 and ERK1/2 in SRB12-p9 cells after treatment with20 μM of curcumin. In our in vivo experimentation, weobserved inhibition of pERK in the curcumin-treated tumorsand inhibition of pSTAT3 in the combined curcumin group.However, tumor heterogeneity and degree of dysplasia canoften confound immunohistochemistry results, dependingon where in the lesion the biopsy was taken. Therefore,it is important to develop serum biomarkers that can beobtained with a simple blood draw. As curcumin is a well-known anti-inflammatory agent, we measured its effects onpooled serum of treated mice and noted a decrease in IL-6 in the topical group compared to the control group. Weobserved that systemic curcumin did not cause a decreasein serum IL-6 levels. However, only three mice in eachgroup were analyzed, and it is possible that statisticallysignificant differences in IL6 levels could be detected uponanalysis of greater numbers of mice in the topical andcombined curcumin-treated groups compared to controlmice.

As curcumin slowed progression of aggressive skin SCCxenografts and inhibited pERK expression, the ERK pathwaymay prove to be a key biomarker in developing topicalpharmaceutical agents that prevent skin SCC tumor growthor recurrence. We observed that the overall reduction inpERK staining in the curcumin-treated tumors was not cell

autonomous but rather manifested as an expansion in areasof very low or no expression, such that focal regions ofintense staining remained. Alternatively, control tumors hadsmaller regions of low staining and a higher number ofintensely staining areas. This indicates that a global reductionof pERK staining was achieved with curcumin treatment,rather than a complete shutdown. [23] confirmed thatphosphorylated ERK is overexpressed in patient skin SCC ina Caucasian population, which further supports our findingsand suggests that pERK may be a useful chemopreventionbiomarker.

Chronic inflammation is linked to both cancer andangiogenesis. The anti-inflammatory properties of curcuminmay contribute to its potential as an effective chemopreven-tive agent. However, curcumin’s systemic anti-inflammatoryeffects (reduced serum IL-6 levels) were more pronouncedin topical curcumin group compared to gavage. Given thesefindings, it was unexpected that tumor growth was inhibitedmore effectively in the gavage group than in the topicalgroup. However, there was no statistically significant differ-ence in tumor volume between the two treatment groups.Despite this data, we speculate that local anti-inflammatoryactivity of topically applied curcumin contributes signifi-cantly to its chemopreventive activity, circumventing its poorsystemic bioavailability.

As curcumin continues to be explored as a chemopre-ventive and therapeutic agent for skin cancer treatment,establishing defined biomarkers upon which curcumin actsto inhibit tumorigenesis is essential. The ERK pathway isan important protein kinase signaling cascade involved incellular proliferation and is activated in carcinogenesis. Inthis study, activated pERK expression significantly increasedin SCC compared to the less aggressive BCC and AK. Ascurcumin has been shown to inhibit activated ERKs incarcinogenesis, the present data suggests that componentsof the ERK pathway may prove to be key biomarkers forcurcumin chemopreventive efficacy in cutaneous SCC.


Conflict of Interests

The authors declare that they have no conflict of interests.

Acknowledgments

This work was supported by the Feist-Weiller Cancer Center.

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